Heat fixing apparatus

ABSTRACT

Apparatus for fixing fusible material such as electroscopic particles upon support material. The apparatus includes a fuser member in the form of an endless belt in contact with the support material being transported. The fusing belt member comprises a highly thermally conductive material which is coated with an electrically insulating material. The support material is electrostatically tacked to the belt member to enhance uniform thermal contact therebetween.

United States Patent lnventor Michael A. Vince Penfield, N.Y. Appl. No.851,826 Filed Aug. 21, I969 Patented June 8, 1971 Assignee XeroxCorporation Rochester, N.Y.

HEAT FIXING APPARATUS 5 Claims, 2 Drawing Figs.

US. Cl 219/388, 95/89, 219/216, 219/349, 219/405, 219/521 Int. Cl. F27b9/06 Field of Search 219/388, 349, 216,405,521, 3479; 263/3; 165/104;95/89; 34/77, 68

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[56] References Cited UNITED STATES PATENTS 3,079,483 2/1963 Codichiniet al 219/388 3,397,303 8/1968 Smith 2l9/388X 3,432,639 3/1969 Hull etal. 219/216 3,515,855 6/1970 Mix, Jr. 219/388 Primary ExaminerVolodymyrY. Mayewsky Attorneys Paul M. Enlow. Norman E. Schrader, James .I.

Ralabate, Ronald Zibelli and Melvin A. Klein ABSTRACT: Apparatus forfixing fusible material such as electroscopic particles upon supportmaterial. The apparatus includes a fuser member in the form of anendless belt in contact with the support material being transported. Thefusing belt member comprises a highly thermally conductive materialwhich is coated with an electrically insulating material. The supportmaterial is electrostatically tacked to the belt member to enhanceuniform thermal contact therebetween.

| g l i PATEN-TEU JUN 8191:

SHEET 1 BF 2 INVENTOR. MICHAEL A. VINCE BY WA (QM ATTORNEY HEAT FlXlNGAPPARATUS This invention relates to heat fixing systems, andparticularly, to improvements in fuser apparatus for particulatematerial such as resinous toner particles, that is used in electrostaticautomatic copiers/reproducers capable of high speed operation.

It has been recognized that one of the preferred methods of applyingheat for fusing the powder image to paper is to bring the powder imageinto direct contact with a hot surface, such as a heated roller.However, in order to produce fused images effectively and efficiently,it has been necessary to utilize relatively large and structurally densefuser rollers which consume large amounts of heat in order to overcomeheat losses effected by the roller supporting structures. Heaterelements for these roller fusers are generally supported interiorly ofone of the rollers which have high temperature gradients needing arelatively large power supply to overcome heat losses as well as forfusing purposes. With the requirement for high fuser heater elementtemperatures comes the need to provide elaborate temperature controls toinsure against equipment protection. Moreover, image offset is normallya problem in the absence of special offset materials, such as, oil whichmust be continuously applied to the roller surfaces. There are otherheat fixing devices not particularly suited for high-speedcopying/duplicating, such as, coiled radiant element heaters withreflectors. These radiant element heaters with reflectors and othertypes such as the recirculating heated air type have the disadvantage ofdissipating a large quantity of heat into the imageenclosure in whichthey are used, heat transfer to the powder image is inefficient, and forthe case of the coiled heater element they present a safety hazardbecause of the exposed element.

It is therefore the principal object of this invention to improve theconstruction of a direct contact fusing device for toner images whichwill require a minimum of heat to accomplish the rapid fusing of tonerimages.

It is another object of this invention to facilitate the handling ofsheet material upon which thermoplastic particles are to be fixed intoand out of contact with heat fusing apparatus without image offset.

These and other objects of the invention are attained by means of adirect contact fusing device in which the toner image is fused byforwarding the sheet of support material bearing toner images upon afuser member in the form of a highly thermally conductive belt which issufficiently heated to fix the image upon the support material. A coronadischarge device is arranged to spray a charge onto the sheet to provideuniform thermal contact between the sheet and belt which is coated withan electrically insulating material to obtain a high quality fix.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is had to the following detaileddescription of the invention to be read in connection with accompanyingdrawings wherein:

FIG. 1 illustrates schematically a xerographic reproducing apparatusadapted for high-speed automatic operation and incorporating a heatfuser constructed in accordance with the invention;

FIG. 2 is an isometric view of the fuser apparatus of the invention. I

For a general understanding of the illustrated copier/reproductionmachine, in which the invention may be incorporated, reference is had toFIG. 1 in which the various system components for the machine areschematically illus trated. As in electrostatic systems such as axerographic machine of the type illustrated, a light image of a documentto be reproduced is projected onto the sensitized surface of axerographic plate to form an electrostatic latent image thereon.Thereafter, the latent image is developed with an oppositely chargeddeveloping material to form a xerographic powder image, corresponding tothe latent image on the plate surface. The powder image is thenelectrostatically transferred to a support surface to which it is fixedby a fusing device whereby the powder image is caused permanently toadhere to the support surface.

in the illustrated machine, an original D to be copied is placed upon atransparent support platen P fixedly arranged in an optical systemgenerally indicated by the reference numeral 10. The image rays areprojected by means of the optical system for exposing the photosensitivesurface of a xerographic plate in the form of a drum generally indicatedby the reference numeral 11.

The xerographic drum 11 is mounted upon the frame of the machine and isadapted to rotate in the direction of the arrow at a constant rate.During this movement of the drum, the light image of the original on theplaten is projected upon the xerographic surface of the drum at anexposure station A. The exposure of the drum surface to the light imagedischarges the photosensitive surface in the areas struck by light,whereby there remains on the belt a latent electrostatic image in imageconfiguration corresponding to the light image projected from theoriginal on the supporting platen. As the drum surface continues itsmovement, the electrostatic image passes through a developing station Bin which there is positioned a developer assembly generally indicated bythe reference numeral 14. The developer assembly 14 deposits developingmaterial onto the drum whereat the material is directed to cascade downover the drum surface in order to provide development of theelectrostatic image. As the developing material is cascaded over thexerographic surface, toner particles in the development material aredeposited on the drum surface to form powder images.

The developed electrostatic image is transported by the drum surface toa transfer station C whereat a sheet of copy paper is moved at a speedin synchronism with the moving drum in order to accomplish transfer ofthe developed image. There is provided at this station a sheet transportmechanism generally indicated at 16 adapted to transport sheets of paperfrom a paper handling mechanism generally indicated by the referencenumeral 18 to the developed image the drum at the station C.

After the sheet is stripped from the drum, it is conveyed to a fuserapparatus according to the present invention generally indicated by thereference numeral 20 whereat the developed transferred xerographicpowder image on the sheet material is permanently affixed thereto aswill be described hereinafter. After fusing, the finished copy isdischarged from the apparatus by a conveyor 21 to a suitable point forcollection externally of the apparatus.

Suitable drive means may be arranged to drive the drum in conjunctionwith exposure of an original to be copied, to effect conveying andcascade of toner material, to separate and feed sheets of paper and totransport the same across the transfer station C and to convey the sheetof paper through the fuser apparatus in timed sequence to produce copiesof the original.

It is believed that the foregoing description is sufficient for thepurposes of this application to show the general operation of anelectrostatic copier using a fuser apparatus constructed in accordancewith the invention.

As shown in FIG. 2, the fuser apparatus 20 is of the heated type throughwhich a sheet of support material, indicated by the reference letter S,is adapted to be conveyed during a fusing operation. The supportmaterial S is conveyed through an entrance slot 22 formed on one side ofthe housing of fuser apparatus and out of an exit slot 23 formed in anopposite wall of the housing. The housing for the apparatus comprisesinsulated walls 24 made of a highly reflective material coated with ahigh thermal insulating material. Within the housing the supportmaterial is conveyed by an endless belt 25 supported for movement on andby a pair of rollers 26 and 27 arranged with their axes in parallel.Shafts for the rollers 26 and 27 may be suitably joumaled and connectedby driving devices such as timing belts or chains to a suitable drivesystem to effect continuous movement of the belt in a directionindicated by the arrow to thereby effect movement of the supportmaterial through the housing of the fuser apparatus. Located between theupper and lower runs of the belt 25 is a heater element 30 which is inthe form of a strip or resistance heater element directed to radiateheat to the belt 25. By being heated in this manner, belt 25 is, ineffect, a fusing member adapted to give up heat uniformly to the supportmaterial S which carries the toner particles in image configuration. I

In' order to achieve good thermal contact uniformly along the entirelength of the contacted belt and support material, the support materialis electrostatically tacked to the belt surface by a corona dischargedevice 40 connected to a variable power source 41. Power source 41 isvariable to enable optimum operation during changes in ambientconditions such as humidity, temperature, etc. To ensure gOOdelectrostatic contact, the belt surface is coated with a very thin layerof electrically insulating material such as Teflon which also serves toprevent the sheet material from sticking to the belt. The Teflon coatingshould be thin enough so that it does not interfere with the heatconduction through the belt and may range from about 0.002 to about0.004 inch. At the end of the belt run, the support material willseparate from the belt due to its natural stiffness. Also, separatingfingers 43 made of suitable material are used to facilitate separationof the sheet material from belt 25.

Belt 25 comprises a highly thermally conductive sheet made of material,such as, copper which possesses some resiliency while exhibiting tensilestrength of a sufficient magnitude to permit its use as a conveyingmember. For insuring that heat will be conducted to the toner particlesto be fused, the belt should be relatively thin, for example,approximately from about 0.010 inch to about 0.030 inch so that heat canbe conducted through the belt with the heater element on the oppositeside from the support material. Each of the rollers 26, 27 arepreferably made of heat resistant, heat insulating material and aresecured to their respective supporting shafts by way of insulating capsor supports.

The distance between the supporting rollers 26, 27 and the length of thebelt 25 may be chosen in accordance with necessary or desirable fusingresults. For instance, the distance between the rollers 26 and 27 may beshortened in the event that the rate of movement of the support materialS through the electrostatic copying/duplicating machine utilizing thefuser apparatus 20 is relatively slow. On the other hand, forelectrostatic duplicating machine arrangements capable of high speedreproduction wherein the speed of movement for the support material isrelatively fast, it may be desirable to extend the distance between therollers 26, 27 to compensate for the speed of the support materialthrough the fuser apparatus.

In operation sheet of support material such as paper is directed ontothe belt 25 image side up and is tacked to the belt surface by coronadischarge device 40 for transfer through the fuser apparatus. Heatcirculating within the fuser apparatus and that which is radiateddirectly from the heater element 30 is applied to the surface of thebelt 25 which has very good thermal contact with the support materialalong the entire length thereof. Since the thickness of the belt 25 isin the order of 0.010 to 0.030 of an inch, it is small enough so thatheat can be conducted through the belt with the heater element locatedon one side of the belt run and a toner image located on the other side.lt has been found that excellent fixes of the toner images includingboth solid area and line copy to moving support material are obtainedwith. temperatures as low as 380 F. at dwell times of about 0.80 to 1.0second.

With the arrangement of the invention, the response time for the heatingelement is relatively fast and, the heat that can be applied to a beltwill be adequate for any copying/duplicating speed. Also the fusingtemperature is independent of the spectral absorption of the toner as inthe case of radiant heaters. In addition, the warm up period to bringthe belt surface to a fusing temperature is relatively short and nostandby periods are required for maintaining the heating elements enerized before or during production runs of an electrostatic mac me. Sincethere IS a minimum loss of heat by way of conduction and radiation, theamount of energy necessary to energize the heating elements may besubstantially reduced. As there is no pressure applied to the image,there is no undesirable offset" of toner particles. In other words, theamount of heat that the heating element 30 must supply is that which isgiven up to the toner particles and the support material plus the verysmall amount of heat that is lost in being transferred from its point ofapplication to the support material.

While the invention has been described with reference to the structuredisclosed herein it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of improvements or the scope of the followingclaims.

What 1 claim is:

1. A heat fusing apparatus for fixing thermoplastic particles carried ona support material in image configuration, said apparatus including athermally insulating housing, means to feed support material bearingheat fusible particles in image configuration into the housing along apredetermined path,

an endless belt member disposed in said housing made of a highlythermally conductive material mounted for carrying and moving saidsupport material along the path and out of the housing,

said belt member being formed therearound with an electricallyinsulating material in laminar form,

electrical discharge means arranged in the sheet path for electricallytacking said support material to said belt surface uniformly along theentire length thereof, and electrical heating means for applying heat tothe side of said belt member opposite that side upon which the imageparticles to be fused and said electrically insulating laminar form arepositioned during movement of said member, the heat being of sufficienttemperature for tackifying and fixing the image upon the supportmaterial.

2. The apparatus of claim 1 wherein said belt member comprises a layerof copper material of a thickness ranging from about 0.010 to about0.030 inch.

3. The apparatus of claim 2 wherein the copper material is covered withan electrically insulating material of a thickness ranging from about0.002 to about 0.004 inch.

4. The apparatus of claim 3 wherein said electrical discharge means isvariable to enable optimum operation during varying ambient conditions.

5. The apparatus of claim 4 including means for removing the supportmaterial from said belt member without causing offset of the heatfusible particles.

1. A heat fusing apparatus for fixing thermoplastic particles carried ona support material in image configuration, said apparatus including athermally insulating housing, means to feed support material bearingheat fusible particles in image configuration into the housing along apredetermined path, an endless belt member disposed in said housing madeof a highly thermally conductive material mounted for carrying andmoving said support material along the path and out of the housing, saidbelt member being formed therearound with an electrically insulatingmaterial in laminar form, electrical discharge means arranged in thesheet path for electrically tacking said support material to said beltsurface uniformly along the entire length thereof, and electricalheating means for applying heat to the side of said belt member oppositethat side upon which the image particles to be fused and saidelectrically insulating laminar form are positioned during movement ofsaid member, the heat being of sufficient temperature for tackifying andfixing the image upon the support material.
 2. The apparatus of claim 1wherein said belt member comprises a layer of copper material of athickness ranging from about 0.010 to about 0.030 inch.
 3. The apparatusof claim 2 wherein the copper material is covered with an electricAllyinsulating material of a thickness ranging from about 0.002 to about0.004 inch.
 4. The apparatus of claim 3 wherein said electricaldischarge means is variable to enable optimum operation during varyingambient conditions.
 5. The apparatus of claim 4 including means forremoving the support material from said belt member without causingoffset of the heat fusible particles.